What chance a dog periodically needs a tree? (5)

I believe the answer is:

cacao

'tree?' is the definition.
(cacao tree is a kind of tree)

I can't explain the remainder of the clue.

(Other definitions for cacao that I've seen before include "Tree for cocoa bean" , "Bean providing chocolate" , "Tree with seeds used to make chocolate" , "Plant" , "Tree yielding chocolate" .)

I've seen this clue in The Times.

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